1. Field of the Invention
The present invention relates to a wafer dividing method including the steps of applying a laser beam having a transmission wavelength to a wafer to thereby form modified layers inside the wafer and next applying an external force to the wafer to thereby divide the wafer into device chips.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a semiconductor wafer to thereby partition a plurality of regions where devices are respectively formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining individual device chips. Conventionally, cutting of the semiconductor wafer is performed by using a cutting apparatus called a dicing saw. However, it is difficult for the dicing saw to cut an optical device wafer having a crystal growth substrate formed of a hard brittle material such as sapphire and SiC. In recent years, therefore, attention has been paid to a technique of using a laser processing apparatus in dividing a wafer into a plurality of devices.
As a laser processing method using the laser processing apparatus, there is disclosed in Japanese Patent Laid-open No. 2005-129607, for example, a technique including the steps of applying a laser beam having a transmission wavelength to the wafer along the division lines to thereby form modified layers (brittle layers) inside the wafer along the division lines and next applying an external force to the wafer along the modified layers having a reduced strength by using an expanding apparatus or the like, thereby dividing the wafer into a plurality of device chips along the modified layers. This laser processing method can eliminate the generation of cutting debris in cutting a wafer by using a cutting apparatus. Further, the space for cutting (laser processing) is very small in this laser processing method, so that the width of each division line can be reduced.